Obama said the program is working the way it was supposed to with "better benefits, stronger protections, more bang for your buck." The assertion was ridiculed by Republicans, with House Speaker John Boehner calling the Affordable Care Act "a train wreck" that he will keep working to repeal.

Obama dismissed the GOP's so-far-futile votes — the House logged its 38th attempt to repeal or scale back the law on Wednesday — with an exasperated sigh and shake of his head during a White House speech. "What I've heard is just the same old song and dance," Obama said of his critics. "We're just going to blow through that stuff and just keep on doing the right thing for the American people."

While the fate of the health care law will play a major role in defining his legacy, Obama has not devoted much time or energy to selling it to the country, speaking on the subject only occasionally as Republicans have pressed a determined campaign to undermine the program. Obama is returning to the subject now because enrollment begins Oct. 1 for subsidized private coverage through new online markets.

Goals of the overhaul are to provide coverage to nearly 50 million uninsured people and restrain skyrocketing costs, but Americans remain skeptical about how their coverage may be affected. Even Obama's allies in the labor unions have turned around their former support of the law out of fears that it will jeopardize benefits for millions of their members by increasing costs. Union leaders also say companies are scaling back work time to avoid providing coverage required for employees who work 30 hours or more. Some labor leaders are now calling for repeal or reform of the law.

Obama launched an impassioned defense of the law at the White House in front of several families who have received refund checks under a provision that requires insurers to spend at least 80 cents of every premium dollar on medical care and quality improvement or reimburse the difference. The president said rebates are being sent for 8.5 million Americans this summer, averaging $100 each. However, much of the money goes to employers who provide insurance and are required to use the money to benefit employees in some way.

Meanwhile, Obama said lawmakers are "trying to make political hay" out of health care and should be worrying about fixing other problems the country faces.

Obama said Americans saved $3.4 billion last year in lower premiums as a result of the efficiencies required by the law. But for many Americans who don't get their insurance through an employer but will be required to buy it next year, the financial impact of the law is still unclear as the government scrambles to launch an online marketplace for them.

Obama noted with approval that some states are anticipating lower premiums because of the health insurance marketplaces that are being set up so consumers can comparison shop for the coverage. Among those states are California, Oregon, Washington and New York.

But in other states there are issues, including Mississippi where in 36 of 82 counties, so far, no insurers are offering plans through the federal online marketplace scheduled to begin enrolling customers Oct. 1. It's unclear whether people in those counties will be held in violation of the law that says they must have coverage.

Not everyone who is uninsured is expected to take the opportunity to get coverage, and that could have vast consequences for the economics of the system. The nonpartisan Congressional Budget Office estimates that about 6 million people of various ages will instead pay the tax penalty for not having insurance in 2014. It's hard to estimate how many of those will be the young and healthy adults that insurers need in the system to offset costs for older, sicker beneficiaries.

Obama acknowledged "glitches" in implementing the sweeping law on a massive industry. Earlier this month the administration announced a one-year delay in a major provision requiring companies to provide coverage for their workers.

Gallup found 52 percent of Americans disapproved of the Affordable Care Act when asked about it in late June. Forty-four percent approved. Gallup found 42 percent saying the law would affect their families' situations in a negative way, 22 percent positive and 33 percent saying it won't make a difference.

Obama urged Americans to think about how the law could provide a free mammogram to catch a grandmother's breast cancer before it spread or help a little girl who could have heart surgery now that there's no lifetime cap on her coverage.

"I recognize that there are still a lot of folks in this town at least who are rooting for this law to fail. Some of them seem to think this law's about me. It's not. I already have really good health care," Obama said, to laughter.